import UIKit

class ModalAnimationController: NSObject, UIViewControllerAnimatedTransitioning {

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        fatalError("Abstract method")
    }

    let cornerRadius: CGFloat = 20
    let offset: CGFloat = 60

    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.4
    }

}

final class ModalPresentAnimationController: ModalAnimationController {

    override func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let fromVC = transitionContext.viewController(forKey: .from),
            let fromView = fromVC.view,
            let toVC = transitionContext.viewController(forKey: .to),
            let toView = toVC.view
            else {
                return
        }

        let offset = self.offset
        let cornerRadius = self.cornerRadius
        let duration = transitionDuration(using: transitionContext)
        let containerView = transitionContext.containerView

        let fromSnapshot = fromView.snapshotView(afterScreenUpdates: true)!
        containerView.addSubview(fromSnapshot)
        fromSnapshot.layer.masksToBounds = true
        fromView.removeFromSuperview()

        containerView.addSubview(toView)
        toView.layer.cornerRadius = cornerRadius
        toView.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]
        toView.layer.masksToBounds = true
        toView.frame = CGRect(x: 0,
                              y: offset,
                              width: containerView.frame.width,
                              height: containerView.frame.height - offset)

        guard let toSnapshot = toView.snapshotView(afterScreenUpdates: true) else {
            return
        }

        containerView.addSubview(toSnapshot)
        toSnapshot.layer.cornerRadius = cornerRadius
        toSnapshot.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]
        toSnapshot.layer.masksToBounds = true
        toSnapshot.frame = CGRect(x: 0,
                                  y: containerView.frame.height,
                                  width: containerView.frame.width,
                                  height: containerView.frame.height - offset)

        toView.isHidden = true

        UIView.animate(withDuration: duration, delay: 0, options: [.curveEaseInOut], animations: {
            fromSnapshot.layer.cornerRadius = cornerRadius
            fromSnapshot.alpha = 0.5
            fromSnapshot.transform = CGAffineTransform(scaleX: 0.9, y: 0.9)
            toSnapshot.frame.origin.y = offset
        }) { _ in
            toView.isHidden = false
            toSnapshot.removeFromSuperview()
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
    }

}

final class ModalDismissAnimationController: ModalAnimationController {

    override func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let fromVC = transitionContext.viewController(forKey: .from),
            let fromView = fromVC.view,
            let toVC = transitionContext.viewController(forKey: .to),
            let toView = toVC.view
            else {
                return
        }

        let offset = self.offset
        let duration = transitionDuration(using: transitionContext)
        let containerView = transitionContext.containerView

        guard let fromSnapshot = fromView.snapshotView(afterScreenUpdates: true),
            let toSnapshot = containerView.subviews.first else {
            return
        }

        containerView.addSubview(fromSnapshot)
        fromView.removeFromSuperview()
        fromSnapshot.frame = CGRect(x: 0,
                                    y: offset,
                                    width: containerView.frame.width,
                                    height: containerView.frame.height - offset)

        toView.isHidden = true

        UIView.animate(withDuration: duration, delay: 0, options: [.curveEaseInOut], animations: {
            fromSnapshot.frame.origin.y = containerView.frame.height
            toSnapshot.layer.cornerRadius = 0
            toSnapshot.alpha = 1
            toSnapshot.transform = CGAffineTransform.identity
        }) { _ in
            toView.isHidden = false
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
    }

}

final class ModalViewController: UIViewController, UIViewControllerTransitioningDelegate {

    override var preferredStatusBarStyle: UIStatusBarStyle {
        return .lightContent
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        transitioningDelegate = self
    }

    @IBAction func tapCloseModal(sender: UIButton) {
        dismiss(animated: true, completion: nil)
    }

}


extension ModalViewController {

    func animationController(forPresented presented: UIViewController,
                             presenting: UIViewController,
                             source: UIViewController)
        -> UIViewControllerAnimatedTransitioning? {
            return ModalPresentAnimationController()
    }

    func animationController(forDismissed dismissed: UIViewController)
        -> UIViewControllerAnimatedTransitioning? {
            return ModalDismissAnimationController()
    }

}